php教程

define

(PHP 4, PHP 5, PHP 7)

define定义一个常量

说明

define ( string $name , mixed $value [, bool $case_insensitive = false ] ) : bool

在运行时定义一个常量。

参数

name

常量名。

value

常量的值;在 PHP 5 中,value 必须是标量( integerfloatstringbooleanNULL)在 PHP 7 中还允许是个 array 的值。

Warning

常量还可以定义为 resource 类型,但并不推荐这样做,因为可能会有不可预知的行为发生。

case_insensitive

如果设置为 TRUE,该常量则大小写不敏感。默认是大小写敏感的。比如, CONSTANTConstant 代表了不同的值。

Note:

大小写不敏感的常量以小写的方式储存。

返回值

成功时返回 TRUE, 或者在失败时返回 FALSE

更新日志

版本 说明
7.0.0 允许 array 的值。

范例

Example #1 定义常量

<?php
define
("CONSTANT""Hello world.");
echo 
CONSTANT// 输出 "Hello world."
echo Constant// 输出 "Constant" 并导致 Notice

define("GREETING""Hello you."true);
echo 
GREETING// 输出 "Hello you."
echo Greeting// 输出 "Hello you."

//  PHP 7 起就可以运行了
define('ANIMALS', array(
    
'dog',
    
'cat',
    
'bird'
));
echo 
ANIMALS[1]; // 输出 "cat"

?>

参见

User Contributed Notes

David Spector 19-Jul-2019 03:03
It may be worth stating that a define function must be executed before its global constant is referenced.

Example:

Abc();
define("TEST", 23);
function Abc()
    {
    echo TEST;
    } // Abc

This code fails with a Notice-level message. TEST is treated here as being the string "TEST".
me at mariusgerum dot de 18-Sep-2018 09:29
You can define constants with variable names (works also with constant values or variables or array values or class properties and so on - as long it's a valid constant name).

<?php
   
   
# Define a constant and set a valid constant name as string value
   
define("SOME_CONSTANT", "NEW_CONSTANT");
   
   
# Define a second constant with dynamic name (the value from SOME_CONSTANT)
   
define(SOME_CONSTANT, "Some value");
   
   
# Output
   
echo SOME_CONSTANT; // prints "NEW_CONSTANT"
   
echo "<br>";
    echo
NEW_CONSTANT; // prints "Some value"
   
   
?>

Needless to say that you'll lose your IDE support for refactoring and highlighting completely for such cases.
No clue why someone would / could actually use this but i thought it's worth mentioning.
Tomas Liubinas 03-Aug-2018 08:40
In PHP 5 it seems it was possible to redefine predefined constants under certain circumstances. The following code will output 42 in PHP 5:

<?php
namespace NS;
define('TRUE', 42, false);
echo
TRUE;
?>

In PHP 7 the output is different (1).
@SimoEast on Twitter 08-Jun-2017 03:10
Not sure why the docs omit this, but when attempting to define() a constant that has already been defined, it will fail, trigger an E_NOTICE and the constant's value will remain as it was originally defined (with the new value ignored).

(Guess that's why they're called "constants".)
Dale Landry 16-Apr-2017 09:45
With php 7 you can now define arrays.

consider the following code:
<?php

define
( "EXPLENATIVES", [1 => "Foo Bar", 2 => "Fehw Bahr", 3 => "Foo Bahr", 4 => "Fooh Bar", 5 => "Fooh Bhar", 6 => "Foo Barr", 7 => "Foogh Bar", 8 => "Fehw Barr", 9 => "Fu bar", 10 => "Foo Bahr", 11 => "Phoo Bar", 12 => "Foo Bawr", 13 => "Phooh Baughr", 14 => "Foogan Bargan", 15 => "Foo Bahre", 16 => "Fu Bahar", 17 => "Fugh Bar", 18 => "Phou Baughr"]);

//set up define methods using mixed values; both array and non-array values
define("NAVBTNS", [EXPLENATIVES, "Nouns", "Verbs", "Adjectives"]);

//function to create a dropdown menu using the EXPLENATIVES array $btn=EXPLENATIVES=assoc_array

function construct_navbar_buttons(){
   
   
$btns = '<ul class="nav navbar-nav">';
                       
    foreach(
NAVBTNS as $button => $btn){
        if(
is_array($btn)){
           
$btns .= '<li class="dropdown">
                        <a class="dropdown-toggle" data-toggle="dropdown" href="?id='
.$btn.'">
                            <i class="glyphicon glyphicon-user"></i> You Dare Say? <i class="glyphicon glyphicon-collapse-down"></i>
                        </a>
                        <ul class="dropdown-menu dropdown-user">'
;
            foreach(
EXPLENATIVES as $key => $button){
               
$btns .= '<li><a href="#">'.$button.'</a></li>';
            }
           
$btns .= '</ul>';
        }else{   
           
$btns .= '<li><a href="#">'.$btn.'</a></li>';
        }
    }
   
   
$btns .= '</ul>';
    return
$btns;
}           

Love this new implementation!

?>
Anonymous 15-Apr-2017 08:33
There's an undocumented side-effect of setting the third parameter to true (case-insensitive constants): these constants can actually be "redefined" as case-sensitive, unless it's all lowercase (which you shouldn't define anyway).

The fact is that case-sensitive constants are stored as is, while case-insensitive constants are stored in lowercase, internally. You're still allowed to define other constants with the same name but capitalized differently (except for all lowercase).

<?php
 
// "echo CONST" prints 1, same as "echo const", "echo CoNst", etc.
 
define('CONST', 1, true);
  echo CONST;
// Prints 1

 
define('CONST', 2);
  echo CONST;
// Prints 2
 
echo CoNsT; // Prints 1
 
echo const; // Prints 1

  // ** PHP NOTICE: Constant const already defined **
 
define('const', 3);
  echo const;
// Prints 1
 
echo CONST; // Prints 2
?>

Why would you use this?

A third party plugin might attempt to define a constant for which you already set a value. If it's fine for them to set the new value, assuming you cannot edit the plugin, you could define your constant case-insensitive. You can still access the original value, if needed, by using any capitalization other than the one the plugin uses. As a matter of fact, I can't think of another case where you would want a case-insensitive constant...
arsicaleksa955 at gmail dot com 30-Mar-2017 09:14
You can also define associative array as constant:

<?php
define
("DB", [
   
"DB_HOST_NAME" => "localhost",
   
"DB_USER_NAME" => "root",
   
"DB_PASSWORD" => "password",
   
"DB_DATABASE" => "db_example"
]);

prin_r(DB);

Array ( [
DB_HOST_NAME] => localhost [DB_USER_NAME] => root [DB_PASSWORD] => password [DB_DATABASE] => db_example )
axew3 at axew3 dot com 16-Feb-2017 09:27
Please, change this,
http://php.net/manual/en/function.define.php#119848
in favor of this one more correct if possible (thank you):

Php 7 - Define: "Defines a named constant at runtime. In PHP 7, array values are also accepted."

But prior PHP 7, you can maybe do this, to pass an array elsewhere using define:

$to_define_array = serialize($array);
define( "DEFINEMYARRAY", $to_define_array );

... and so ...

      $our_array = unserialize(DEFINEMYARRAY);

print_r($our_array);
axew3 at axew3 dot com 05-Sep-2016 08:46
Php 7 - Define: "Defines a named constant at runtime. In PHP 7, array values are also accepted."

But prior PHP 7, you can maybe do this, to pass an array elsewhere using define:

$to_define_array = serialize($array);
define( "DEFINEANARRAY", $to_define_array );

... and so ...

$serialized = DEFINEANARRAY; // passing directly the defined will not work
      $our_array = unserialize($serialized);

print_r($our_array);
ivan at aleksandrow dot net 12-Apr-2016 08:51
In case someone else is curious like me, defining a variable to "false", actually undefining it:

define ("A", false);

if (defined("A"))
 echo A;

will echo nothing. Useful, when you need to define, for example, log and keep definition without actually having it defined.
ayyappan dot ashok at gmail dot com 12-Apr-2016 06:58
define("THIS+IS_A_TEST","This is a test");
echo THIS+IS_A_TEST;

//It results 0 but with NOTICE ERROR

Rule : Don't use Operators as constant.
swisschocolate at cmail dot nu 13-Feb-2016 11:35
I think worth mentioning is that define() appears to ignore invalid constant names.
One immediate implication of this seem to be that if you use an invalid constant name you have to use constant() to access it and obviously that you can't use the return value from define() to tell you whether the constant name used is invalid or not.

For example:
$name = '7(/!§%';
var_dump(define($name, "hello")); // outputs bool(true)
var_dump(constant($name)); // outputs string(5) "hello"
fernandopsilveira at yahoo dot com dot br 23-Sep-2015 05:05
Just like define(), defined() will check for constants exactly as specified. So, if you want to check a constant in a namespace, you will need to specify the namespace in your call to defined(), even if you're calling defined() from within a namespace.

To check for a defined constant within current namespace, you can use __NAMESPACE__ magic variable:

<?php
namespace mytest;

define('mytest\CONSTANTINE', 'value');

if (
defined(__NAMESPACE__ . '\CONSTANTINE')) {
    print
"Constant is defined and is valued " . CONSTANTINE;
}
?>
ravenswd at gmail dot com 22-Feb-2015 03:11
Be aware that if "Notice"-level error reporting is turned off, then trying to use a constant as a variable will result in it being interpreted as a string, if it has not been defined.

I was working on a program which included a config file which contained:

<?php
define
('ENABLE_UPLOADS', true);
?>

Since I wanted to remove the ability for uploads, I changed the file to read:

<?php
//define('ENABLE_UPLOADS', true);
?>

However, to my surprise, the program was still allowing uploads. Digging deeper into the code, I discovered this:

<?php
if ( ENABLE_UPLOADS ):
?>

Since 'ENABLE_UPLOADS' was not defined as a constant, PHP was interpreting its use as a string constant, which of course evaluates as True.
daevid at daevid dot com 19-Feb-2014 05:45
Be aware that undefined constants are not evaluated the same as undefined variables (which is frustratingly counter-intuitive)...

$ php -a

php > if (!DO_IT) echo "don't do it\n"; else echo "do it\n";
do it

php > var_dump(DO_IT);
string(5) "DO_IT"

php > if (!$DO_IT) echo "don't do it\n"; else echo "do it\n";
don't do it

php > var_dump($DO_IT);
NULL

You have to specifically check for the definition like so...

php > if(!defined('DO_IT') || (defined('DO_IT') && !DO_IT))echo "don't do it\n"; else echo "do it\n";
don't do it

*sigh*
php at richardneilll dot org 14-Jul-2013 12:15
In PHP,  define does not have the same gotchas as the C-preprocessor. E.g.

//In PHP:
define ("x", 5+2);    //x is evaluated as 7
echo 3 * x;             //This is 21, as you'd expect.

//But in C:
#define x   5+2;       //x is the string "5+2", substituted later.
printf ("%d",  3*x);  //This is 17.
New Social Life 17-Aug-2012 02:59
I want to show you how to define multiple things at once

just use this small function: ( i'm trying to do it even smaller... but i think is small enough )

<?php function ...define($a){foreach($a as $k => $v)define($k, $v);} ?>

usage example:

<?php
...define
(array(
   
"second" => 1,
   
"minute" => 60,
   
"hour" => 3600,
   
"day" => 86400,
   
"week" => 604800,
   
"month" => 2592000, // 30 days month
   
"year" => 31536000,
   
"year2" => 31622400
));
?>

PLEASE NOTE:
there AREN'T three points, there is the three points CHARACTER, to be sure, just copy paste my code
kriscraig at php dot net 23-Mar-2012 09:47
Some people like to have an ambiguous, engine-agnostic database include specified by assigning a single config variable to one of a series of constants.  Unfortunately, this can easily become needlessly clunky if these defines are handled in an included config.php file, since more than one hook will throw an ugly "already defined" error.

Here's a simple way to accomplish this architectural model without having to create a bunch of clumsy sanity checks that compromise scalability:

<?php

/* Available databases.  --Kris */
$dbengines = array();
$dbengines[] = "mysql";
$dbengines[] = "mysqli";
$dbengines[] = "pgsql";

foreach (
$dbengines as $engine )
{
    if ( !
defined( "_" . strtoupper( $engine ) . "_" ) )
    {
       
define( "_" . strtoupper( $engine ) . "_", $engine );
    }
}

/* Which database engine shall we use?  --Kris */
$sql_type = _MYSQLI_;

?>
Then, somewhere later in the stack....

<?php

/* Include the file with the desired sql class.  --Kris */
require_once( $sql_type . ".php" );

/* Now you can use the same code for any supported db engine.  --Kris */
$sql = new sql();
$res = $sql->query( .... );
phen at adnerdum dot org 06-Jul-2011 01:32
To clear up a few thing:
Integers with 0 in front work. But since PHP (and many other languages) handle them as octal values, they're only allowed a range of 0-7:

<?php
 define
('GOOD_OCTAL', 0700);
 
define('BAD_OCTAL', 0800);

 print
GOOD_OCTAL;
 print
'<br>';
 print
BAD_OCTAL;
?>

Result:
448
0

---------------------------------------

Furthermore,

writing the constant name without the quotation-marks (as mentioned in the notes) throws an E_NOTICE and should be avoided!

<?php
 define
(TEST, 'Throws an E_NOTICE');
?>

Result:
Notice: Use of undefined constant TEST - assumed 'TEST'
kobrasrealm at gmail dot com 10-Jun-2011 06:31
When going back to rewrite code, it might be tempting to have a constant &reference a variable, but it doesn't work.

<?php
header
("Content-type: text/plain");
$variable = "value";
define("MYCONSTANT", &$variable);
  echo
$variable."\n";
  echo
MYCONSTANT."\n";
  echo
"------\n";
$variable = "different";
  echo
$variable."\n";
  echo
MYCONSTANT;
?>

Produces this:

value
value
------
different
value

I doubt it's supposed to work, either. :)
Jamie 01-Mar-2011 01:24
This is obvious, but easy to forget: if you include a file, the include file can only make use of constants already defined. For example:

<?php
define
("VEG","cabbage");
require(
"another file");
define("FRUIT","apple");

// "another file":
echo VEG; // cabbage
echo FRUIT; // FRUIT
?>
andreas at cap-systems dot com 05-Feb-2011 04:54
Constant name must not written as string. The following code works also:

<?php
define
(MY_NAME, 'value');
define('ANOTHER_NAME', 'value2');

if(
defined('MY_NAME')) {
  echo
MY_NAME . '<br />';
}

if(
defined('ANOTHER_NAME')) {
  echo
ANOTHER_NAME . '<br />';
}

echo
MY_NAME . '<br />';
echo
ANOTHER_NAME . '<br />';
?>

Output:
value
value2
value
value2

Tested with:
- PHP 5.3.1 on XAMPP on Windows Vista (local)
- PHP 5.2.42 on Apache 2.0 on Linux (remote)
- PHP 5.2.12 on Apache 2.0 on Linux (remote)
angelos at unkreativ dot org 09-Jan-2011 01:18
Something I found out the "hard" way today: integers starting with 0 won't work.
<?php
define
('SOMECONSTANT', 09900);
var_dump(SOMECONSTANT);
?>
Produces int(0)

<?php
define
('SOMECONSTANT', 9900);
var_dump(SOMECONSTANT);
?>
Produces int(9900)
toph at farmer corp dot c om 16-Oct-2010 02:51
Hi,

Here is a trick to use constants within the heredoc notation.

<?php
define
('MY_CONSTANT','foo bar')
$cst = 'cst';
function
cst($constant){
    return
$constant;
}

$string = <<<EOF
My constante MY_CONSTANT : {$cst(MY_CONSTANT)} ...
EOF;
echo
$string;
?>

That will echo :

My constante MY_CONSTANT : foo bar ...

As you can use function within the heredoc notation the idea is to use a fonction to return the value of the constant.
Be carefull, to use a function, it's necessary to declare the name of the function as a variable and to use that varaible during the "call" of the constant.

It works for me and doesn't seem too messy.

Hope that will help.
rush at bigup dot com dot pa 10-Aug-2010 10:23
Just in case:

You cannot set a constant to be a class.  For example:
define ("WSDLCLIENT",new soapclient(WSDLSERVER, 'wsdl'));

You cannot do this.
chris at peeto dot net 25-Mar-2010 07:15
The value of a constant can be the value of another constant.

<?php

define
("NEW_GOOD_NAME_CONSTANT", "I have a value");
define("OLD_BAD_NAME_CONSTANT", NEW_GOOD_NAME_CONSTANT);

echo
NEW_GOOD_NAME_CONSTANT; // current
echo OLD_BAD_NAME_CONSTANT; // legacy

?>
bohwaz.net 15-Aug-2009 05:54
Note that define don't care at all about the constant name, you can give everything as a constant name, even if the PHP documentation says that the allowed characters are [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*

Just try this :

<?php define('anything::()$', 'test'); ?>

You won't be able to access this constant though, it will throw a parse error, either through constant() or define(), but if you do that :

<?php print_r(get_defined_constants()); ?>

You will see that the constant is registered at the end of the array. Yes that's totally useless. But you can try other things that will work with constant() :

<?php define('...', 'test'); echo constant('...'); ?>

Will echo 'test'. Yeah that's a pretty strange behavior.

And please note that defining object constants outside of objets don't work :

<?php
class myObject { }
define('myObject::CONSTANT', 'test');
?>
Anonymous 19-Jul-2009 10:31
My notice to: redeclare define -  it is possible

php -v

--> PHP 5.2.6-3ubuntu4.1 with Suhosin-Patch 0.9.6.2
Zend Engine v2.2.0, Copyright (c) 1998-2008 Zend Technologies
php -r "define('TEST','foo',true);
var_dump(TEST);
define('TEST','bar');
var_dump(TEST);"

string(3) "foo"
string(3) "bar"

greetings
sixd at php dot net 17-Jul-2009 02:24
A note on redefining:

Constants can't be redefined:

$ php -r "define('A', 1); var_dump('A'); define('A', 2); var_dump('A');";
string(1) "A"
PHP Notice:  Constant A already defined in Command line code on line 1
string(1) "A"

But using the case insensitive setting shows that the internal
representation is lower case:

$ php -r "define('A', 1, true); var_dump('A'); define('A', 2); var_dump('A');";
string(1) "A"
string(1) "A"

Note the lower case 'a' in the second define() here:
$ php -r "define('A', 1, true); var_dump('A'); define('a', 2); var_dump('A');";
string(1) "A"
PHP Notice:  Constant a already defined in Command line code on line 1
string(1) "A"
danbettles at yahoo dot co dot uk 14-Apr-2009 11:56
define() will define constants exactly as specified.  So, if you want to define a constant in a namespace, you will need to specify the namespace in your call to define(), even if you're calling define() from within a namespace.  The following examples will make it clear.

The following code will define the constant "MESSAGE" in the global namespace (i.e. "\MESSAGE").

<?php
namespace test;
define('MESSAGE', 'Hello world!');
?>

The following code will define two constants in the "test" namespace.

<?php
namespace test;
define('test\HELLO', 'Hello world!');
define(__NAMESPACE__ . '\GOODBYE', 'Goodbye cruel world!');
?>
Aldonio 27-Mar-2009 08:24
This code will define every key of an array, and if its a multidimentional array it will define it as parent_child1_child2_etc.

<?php
function define_array( $array, $keys = NULL )
{
    foreach(
$array as $key => $value )
    {
       
$keyname = ($keys ? $keys . "_" : "") . $key;
        if(
is_array( $array[$key] ) )
           
define_array( $array[$key], $keyname );
        else
           
define( $keyname, $value );
    }
}
?>
ceo at l-i-e dot com 11-Mar-2009 02:04
In PHP 4.4.9, you cannot use certain names for constants.

Specifically, reserved words such as 'PRINT', 'IF', etc.

Oddly enough, you get different behaviour for some:

<?php
define
('IF', 42);
echo
"IF: ", IF, "<hr />\n";
?>

yields PHP Parse error:  syntax error, unexpected T_IF

<?php
define
('PRINT', 13);
echo
"PRINT: ", PRINT, "<hr />\n";
?>

yields PHP Parse error:  syntax error, unexpected ')'

Not sure if this is still true in PHP 5 or not, but it's worth noting if it is.
Anonymous 09-Mar-2009 01:03
With php 5.30 it is possible to make some "restrictions", in case u use namespaces...
The following function allows only uppercase and, if 3 param isset, gives E_USER_ERROR instead of E_NOTICE:

<?php
namespace bla;

function
define($c,$v,$x=false) {
   
$c = strtoupper($c);
    if (!
defined($c)) {
       
// not to use \define here, as the syntax highlighting does not work correctly here...
       
return define($c, $v, true);
    } else if (
$x == true) {
       
trigger_error('setting constant "'.$c.'" is not allowed', E_USER_ERROR);
    }
    return
null;
}

define('PHP_VERSION', '1');
define('PHP_VERSION', '1') || trigger_error('constant already defined', E_USER_NOTICE);
define('PHP_VERSION', '1', true);
?>
jv at vip dot ie 08-Mar-2009 04:14
Probably the most efficient way of creating a constant array is to put it in a function like this:

<?php
function my_const_arr()
{
   return array
   (
     
'key1' => 'val 1',
     
'key2' => 'va' 2'
   );
}
?>

Then use at will like so...
<?php $my_const_arr = my_const_arr(); ?>
usuroer dot king at hotmail dot co dot uk 08-Mar-2009 04:15
Referring to "This-Is-A-Test" constant below.

When echoing it the script thinks you performing a series of minus (subtraction) thus since THIS and IS, A, TEST are not defined they are 0 by default. So 0-0-0-0 = 0.

As explained that a hyphen cannot be used within a variable.
downwind at web dot de 01-Feb-2009 08:48
I'm reffering to the note below by mittiprovence.

The described behavior has nothing to do with the fact that there is a constant in the condition.

Comparing a non-numeric string to the integer 0 by using == will return true, since the string will be casted to integer - which will be zero. If your string starts with a number, it will be castet to an integer with the number as value.

To avoid the described behavior, you should use === instead of ==.

Finally, the behavior discribed by mittiprovence is exacly the expected behavior as defined in the manual.

For further information read the manual:

http://www.php.net/manual/en/types.comparisons.php

http://www.php.net/manual/en/language.operators.comparison.php

http://www.php.net/manual/en/language.types.string.php #language.types.string.conversion

<?php

if (0 == "some string") { // is true
echo "0 == 'some string'";
}

if (
1 == "some string") { // is false
echo "1 == 'some string'";
}

if (
1 == "1 some string") { // is true
echo "1 == '1 some string'";
}

if (
0 === "some string") { // is false
echo "0 === 'some string'";
}

?>
eparkerii at carolina dot rr dot com 22-Oct-2008 12:01
Found something interesting.  The following define:

<?php
define
("THIS-IS-A-TEST","This is a test");
echo
THIS-IS-A-TEST;
?>

Will return a '0'.

Whereas this:

<?php
define
("THIS_IS_A_TEST","This is a test");
echo
THIS_IS_A_TEST;
?>

Will return 'This is a test'.

This may be common knowledge but I only found out a few minutes ago.

[EDIT BY danbrown AT php DOT net: The original poster is referring to the hyphens versus underscores.  Hyphens do not work in defines or variables, which is expected behavior.]
jan at webfontein dot nl 27-Jul-2008 05:20
For translating with variables and define, take also a look on the constant() function.

Example :

<?php
define
('PAYMENT_IDEAL',"iDEAL Payment ( NL only )");
define('PAYMENT_MASTERCARD',"Mastercard Payment ( international )");

$payparam='MASTERCARD';

echo
constant("PAYMENT_$payparam");

// output :
// Mastercard Payment ( international )
?>
thscheer at web dot de 20-Jun-2008 02:18
How to define an array as constant with define?

there is a simple way to define an array of values as constant...

just

define ("constant-name","value1,value2,value3,value4");

$t_array = preg_split('/,/', constant(constant-name), -1, PREG_SPLIT_NO_EMPTY);

var_dump($t_array);

array(4) { [0]=> string(6) "value1" [1]=> string(6) "value2" [2]=> string(6) "value3" [3]=> string(6) "value4" }

Now you can iterate over the array defined as constant ...
ceo at l-i-e dot com 05-May-2008 08:30
I'm not sure if it's version dependent, but apparently this works:
define('APPLICATION_NOW', time());

This can be quite handy for time-dependent code...

You can then do:
class foo {
  $private now = APPLICATION_NOW;
}

and have a consistent time-stamp across the application, which is nice.

Works for me in 5.2.5

I didn't think it worked before...
jason@sitehatchery dot com 24-Apr-2008 11:28
You can store your constant as the value of a variable like this:

$variable=VARIABLE;

To access the constant, do this:  constant($variable).

Beware: if your variable changes, then you loose your reference to the constant - but the constant itself will not change.

I've found this especially useful for storing the constant string   (i.e. VARIABLE) in a database.
rayro at gmx dot de 15-Sep-2007 02:53
just a note to the previous post by e s lin d sey at g mail dot co m:

Well as u said, it is not the best workaround. To resolve this "Problem" without getting incredible loss of performance, you are able to make the use of "variable functions" like "variable variables":

<?php
$def
= 'constant';
$string = <<<END
    This is PHP running on<br />
   
{$def('PHP_OS')}
END;
var_dump($string);
?>

In this example we make use of the "constant" function which is builtin, and it will output:

string(37) " This is PHP running on
WINNT"

Tested on PHP 5...
Best regards
e s lin d sey at g mail dot co m 13-Aug-2007 01:38
Constants can't be referenced from within quotes or (more importantly IMHO) from within HEREDOC syntax. This is a huge drawback in my opinion. Here's two of my workarounds:

<?php

//PHP5 only -- more efficient
$constarray = get_defined_constants(true);
foreach(
$constarray['user'] as $key => $val)
    eval(
sprintf('$_CONSTANTS[\'%s\'] = \'%s\';', addslashes($key), addslashes($val)));

//PHP4+ -- less efficient because it defines (potentially) hundreds of unnecessary constants
foreach(get_defined_constants() as $key => $val)
    eval(
sprintf('$_CONSTANTS[\'%s\'] = \'%s\';', addslashes($key), addslashes($val)));

?>

Now you can refer to your defined constants using the $_CONSTANTS array. Note that because this is NOT a superglobal, a few caveats apply:

<?php

//run code snippet here to define $_CONSTANTS in global scope...

$mv = $_CONSTANTS['FOO']; //works

function my_function1()
{
   
$mv = $_CONSTANTS['BAR']; //doesn't work! not defined!
}

function
my_function2()
{
    global
$_CONSTANTS;
   
$mv = $_CONSTANTS['BAR']; //ah, this works!
}

?>

I realize this is not ideal, either for performance or for convenience of being able to refer to constants without regard to scope, but it is a workaround that works. Depending on your application, it may be easier to shift your paradigm a bit and use the following method instead, declaring your constants as variables first:

<?php

//first, define our constants...
$_CONSTANTS['FOO'] = 'bar';
$_CONSTANTS['BAR'] = 'foo';

//now, turn them into real constants...
foreach($_CONSTANTS as $key => $val)
   
define($key, $val);

//now, you can use either format to refer to a constant
print($_CONSTANTS['FOO']);   //prints 'bar'
print(FOO);                  //prints 'bar'
print("$_CONSTANTS['FOO']"); //prints 'bar'
                             //prints 'blah bar blah'
print <<<EOF
  blah {$_CONSTANTS['FOO']} blah
EOF;

?>

Hope this helps some of you out there, I know being able to utilize my constants in HEREDOC helped me a ton!
smifffy at smith-net dot org dot uk 25-Jul-2007 04:23
a basic function to auto assign a numeric value that increase by itself each time - used in some permission style scripts

<?php
function define_bitwise($constant_name, $reset = False)
{
    static
$bitwise_next = 1;

    if (
$reset === True )
    {
       
$bitwise_next = 1;
    }

   
define($constant_name, $bitwise_next);
       
   
$bitwise_next += $bitwise_next;
}
?>

when reset it set to True, resets that value to 1 and starts afresh
creeves at dja dot com 19-Jul-2007 06:59
Intersting to note:

I found this in php5 on windows

If you try to unset a constant (which you cant but maybe you have a Jr. programmer or something).  The error message that is thrown is:

<?php
define
("SOME_CONSTANT", true);
unset (
SOME_CONSTANT);
?>

Parse error: parse error, unexpected ')', expecting T_PAAMAYIM_NEKUDOTAYIM
nl-x at bita dot nl 09-Jul-2007 10:34
Watch out. You can define a new constant with the name NULL with define("NULL","FOO");. But you must use the function constant("NULL"); to get it's value. NULL without the function call to the constant() function will still retrieve the special type NULL value.
Within a class there is no problem, as const NULL="Foo"; will be accessible as myClass::NULL.
stangelanda at arrowquick dot com 31-Dec-2006 06:59
An improvement on the function from bobbykjack at yahoo dot co dot uk on the concept by richard dot quadling at bandvulc dot co dot uk:
<?php
function adefine($constant_name, $value=null) {
    static
$increment = 0; // 1 for bitmask

   
if (is_null($value)) {
       
define($constant_name, ++$increment); // $increment=$increment<<1 for bitmask
   
} else {
       
define($constant_name, $value);
        if (
is_numeric($value)) {
           
$increment = $value;
        }
    }
}
?>
If you pass it a second argument it defines it normally, and resets the increment if the value is numeric.  This way the function can replace define, and you can reset the counter for a new set of constants.
<?php
adefine
('RULE_CALLBACK_FORMAT', 1); // 1
adefine ('RULE_CHANGE_CALLBACK_ON_ERROR'); // 2
adefine ('RULE_CHANGE_COMPARE_DATE'); // 3
adefine('KEYWORD', 'hodgepodge'); // hodgepodge <-- defined normally
adefine ('RULE_CHANGE_ON_DATE'); // 4

adefine ('ERROR_DESC', 1); // 1 <-- Counter reset
adefine ('ERROR_EXPECTED_RESULT'); // 2
?>
radovan dot biciste at managestar dot com 06-Nov-2001 08:45
Wonder how to work with variable which name is stored in a constant?
Here it is:
<?php
define
("VAR_NAME","test");
// assigning value
${VAR_NAME} = "value";
// getting value back
echo ${VAR_NAME};
?>

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